Automated clinical analyzers have recently enjoyed widespread use by diagnostic laboratories for the rapid and reliable detection of analytes in a variety of biological samples. Analyzers are routinely used to perform a wide variety of assays, most of which involve immunoassays where the high affinity and selectivity of an antibody for its antigen is exploited.
Most of the recent efforts of the diagnostic community have focused on the development of products for either high-throughput clinical laboratories or single-use “point-of-care” settings. High throughout screening (HTS) is a mature area of diagnostics that is generally served by large, expensive and complex analyzers. Analyzers with very high throughput capabilities are usually modular in form, with each separate module performing a single step of the assay. For example, modules commonly exist for fluid handling, incubating, vortexing, transport, and reading and analyzing the assay result. The modules are then robotically interconnected to provide full automation. Alternatively, some HTS analyzers are designed as a single unit, with multiple subsystems integrated into a common instrument. Such analyzers are more compact than their modular counterparts and usually have a somewhat reduced throughput, but still require a significant amount of laboratory space.
U.S. Pat. No. 6,042,786 discloses one such system, in which a single pipette in linear motion is used to aspirate and dispense samples and reagents. This system has a throughput of approximately 200 samples per hour and includes on-board reagent storage and refrigeration. In U.S. Pat. No. 5,885,530, an immuno-analyzer is disclosed that fully automates the handling and analysis of a bead-based heterogeneous assay system. This complex system features a centrifugal bead wash station and a re-usable sample dilution well. It is favored for clinical settings in which a high throughput of heterogeneous assays is required. In another instance of the prior art, U.S. Pat. No. 6,649,182 describes an analyzer for use with a biochip that is deposited with an array of receptors for different analytes. This system is useful for screening a large number of samples for the presence of very high number of analytes.
At the other end of the diagnostic spectrum lies point-of-care testing, in which simple, disposable cartridges are commonly used to perform a rapid screening assay. These devices are designed primarily for “doctor's office” or “bedside” applications in which a very low throughput of samples is encountered. Point-of-care screening has traditionally been performed using disposable lateral-flow assay devices. A lateral-flow assay device typically contains a sample pad, a conjugate pad, a membrane with reagent lines and an absorptive pad. The sample is added to the sample pad and flows through the conjugate pad, where it interacts with analyte-specific labeled antibodies, forming a bound complex. The bound complex then flows through a porous membrane to one or more reagent lines, at which point the bound complex and unbound analyte binds. The presence of a coloured line at the reagent indicates a positive result. The sample continues to flow through the membrane to the absorbent pad, where it is absorbed. It is commonplace for a second control reagent line to be added to confirm the event of a positive result. Such a device is used in U.S. Pat. Publication No. 2002/0146346A1, where a single lateral flow platform is used to screen for a panel of several drugs of abuse. Such devices are useful for qualitative analysis, but are generally not useful for obtaining reliable quantitative results.
Recently, the field of point-of-care diagnostics has evolved beyond simple qualitative devices to quantitative or semi-quantitative analyzers that accept single-use, disposable sample cartridges. Most of these analyzers rely on cartridges with advanced internal sample processing capabilities, including sample delivery, reagent delivery, washing, incubation and the absorbance of waste fluids. Microfluidic technologies are often employed to achieve these functions, with capillary action or centrifugal forces used to provide metered fluid delivery. Alternatively, capillaries can be used as valve stops, beyond which fluid flow is only made possible following the application of sufficient air pressure from by an external means.
An example of such a cartridge is provided by U.S. Pat. Publication No. 2003/0170881A1, in which a disposable cartridge for point-of-care settings is disclosed. The cartridge is placed by the operator in the analyzer, which performs an enzyme-based immunoassay for a given analyte. Upon completion of the assay, results are read via electrical means, such as the amperometric or potentiometric reading of thin films, which advantageously reduces the design complexity, size and cost of the analyzer.
Another suitable cartridge for point-of-care diagnostics is described in U.S. Pat. Publication. No. 2003/0180815, in which a simple and disposable lateral flow assay device is adapted for use in an analyzer. Unlike conventional colourimetric lateral flow assay devices, this invention uses an enzyme for the dissolution of a polymer membrane coating an electrode, providing an electrical measurement of the assay result. The cartridges can therefore be inserted into a simple reader that employs a capacitive measurement for the determination of assay results.
Despite the advances made in serving HTS markets and “point-of-care” settings, the needs of small clinics with low-to-moderate throughput requirements have been largely overlooked. An excellent example of these clinics is the so-called “point-of-collection” clinic, in which client or patient samples are routinely collected for analysis. Examples of such medical clinics include cancer, fertility and cardiac clinics and also therapeutic treatment clinics including methadone maintenance clinics and pain management clinics. Another example of a point-of-collection setting is workplace drug testing performed by a large employer on a routine basis. Other examples of small clinics include specialized non-medical laboratories such as food testing or environmental testing laboratories, where periodic sample collection is routinely employed as a safety measure.
In its most efficient form, on-site testing enables a small clinic to obtain test results within minutes. In the case of medical point-of-collection clinics, the rapid availability of the results reduces the costs of testing and allows the physician to provide a much higher standard of care, responding immediately to changes in the patient's condition. On-site testing also assists small non-medical laboratories to enable rapid testing and offers the ability to easily customize and vary the assay test plan.
The needs of smaller sized clinics are therefore likely to be best met by an inexpensive analyzer that is easy to operate. A step towards this goal has been taken in the prior art by the development of microplate-based automated analyzer systems. Such analyzers employ an array of microwells to perform the assay reaction on a per-assay and per-sample basis.
Microplates for such a use are commercially available in a number for formats, the most commonly used format at present being the 96-well 8×12 microplate. Other popular microplate formats provide much more wells are the 384 and 1538-well microplates. For all of such microplates, the many of the physical dimensions are required to meet an industry standard that promotes the usage of a single format across a wide range of analyzer and instruments.
Although microplate-based liquid handling systems and single-function microplate systems such as microplate washers, incubators, agitators and readers are well known in the prior art, only a few examples of compact fully-automated microplate analyzers have been disclosed. One example of a microplate-based analyzer system is provided by U.S. Pat. No. 5,104,621 issued to Pfost et al., where an automated analyzer employing microplates for the purpose of conducting ELISA assays is disclosed. The analyzer employs a number of integrated subsystems to provide a versatile laboratory instrument for the automation and control of assays. Reagents are dispensed from a bulk dispenser into the wells of a microplate. The microplate, reagents and consumables are all housed in a common two-dimensional plane.
Another analyzer that uses a more complex spatial layout of subsystems is disclosed in U.S. Pat. No. 5,122,342 issued to P. F. McCulloch et al., where a magazine containing a plurality of assay-specific microplates is housed within the analyzer. Samples are loaded into the analyzer and are identified by a machine-readable barcode. The analyzer is programmed by the operator to perform a series of assays on a set of samples, and assay reactions are performed in a microplate format, with a different microplate for each assay. Reagents are dispensed from a bulk internal storage apparatus via multichannel plungers. A key aspect of this patent is that the identity of the individual microplate carriers is confirmed while moving the microplate to a given subsystem by reading an identifying barcode affixed to each assay-specific plate carrier.
In another example of microplate analyzers in the prior art, U.S. Pat. No. 5,650,122 provides an automated system for performing an enzyme-linked immunosorbent assay (ELISA). The analyzer automates the processing of two ELISA-based microplates, incorporating sample pipetting, incubation, washing and optical absorbance reading into a single instrument. Although the sample is directly pipetted (and diluted, if necessary) by the analyzer into the microplate, the placement of the sample test tubes is done by the operator and is susceptible to transcription errors. Such an analyzer requires a high degree of skill by a trained operator for proper quantitative analysis.
A fourth microplate-based analyzer system is described in US Patent Application 2002/0006362 A1 (Ohta et al.). This microplate-based analyzer system improves over the prior art by providing a more compact and efficient system. As in the aforementioned microplate-based analyzers, this system employs bulk reagent storage and a liquid transfer station for dispensing reagents from bottles to microplate wells where the assay reaction occurs.
A fifth microplate-based analyzer is commercially available from BMG as the NOVOstar system, which is a compact analyzer system that allows the operator to load both a reagent and a measurement microplate, the latter containing pre-dispensed sample. An internal pipetting system enables the transfer of reagents from the reagent microplate to the reaction microplate, where the assay reaction is initiated. The system further includes means for agitation, incubation, microplate washing, dispensing of additional stored bulk reagents, and optical detection. The analyzer is sold as a fully automated tool for research laboratories.
Unfortunately, none of the four aforementioned microplate-based analyzer systems are designed for use in a small clinical setting. The analyzers all assume a high degree of operator skill, especially for providing such functions as the programming of assay protocols, inventory management of internally-housed reagents, frequent maintenance, and the correct placement of samples within the analyzer. Such requirements represent a large drawback for use in a small clinical setting, where speed and simplicity are crucial.
As mentioned above, a critical requirement for most small clinics is the ability for unskilled personnel such as secretaries or nurses to operate diagnostic analyzers for on-site testing with minimal training. Small clinics often cannot afford the added expense of employing skilled technicians to run a clinical laboratory. Furthermore, there may be regulatory issues that preclude the employment of trained staff in small clinics. This requirement has important consequences for the handling of samples for analysis. Provisions must be made in the analyzer (and cartridge if one is used) to protect against sample transcription errors, which can lead to erroneous results and liability concerns. Equally important is the need for the design of the analyzer to minimize the possibility of unskilled personnel being exposed to potentially hazardous samples.
Due to the lack of analyzers designed specifically for small clinics, clinicians are often forced to choose between using high-throughput analyzers or single-use, point-of-care devices for on-site testing. Unfortunately, the high purchase cost and need for skilled technicians makes HTS analyzers inappropriate and unaffordable for most small clinical settings. Also, as previously discussed, HTS analyzers typically enable sample throughput in excess of several hundred samples per hour, which is far beyond the requirements of small clinics and laboratories. The usefulness of point-of-care diagnostic devices in small clinics is also limited. Although simple disposable devices such as lateral flow assays are useful in very low-throughput applications where a qualitative result is desired, they fail to provide the necessary accuracy for the majority of small clinics that require a quantitative result.
The role of the operator in interpreting the assay result is also problematic in many clinical settings. In addition, manual devices do not automatically provide an electronic record of the test result that can be remotely achieved on a computer system. Although point-of-care analyzers surmount many of these problems, their throughput and need for frequent loading and unloading of the instrument make them impractical for small clinics or laboratories with moderate sample throughput. Unfortunately, many of the cartridges used in such instruments lack the assay diversity needed to perform a wide range of tests. The use of a sample cartridge often prohibits sample dilution, which may be necessary for some assays.
Point-of-care analyzers also often suffer from poor assay repeatability due to poor tolerances in the manufacture of cartridge parameters or insufficient accuracy when dispensing fluids. The repeatability is often further compromised by the lack of sufficient calibrators or controls. This poor repeatability leads to a significantly larger coefficient of variation in the assay result, which limits the dynamic range and precision of the assay. Perhaps most importantly, the use of complex, proprietary, single-sample, single-test disposable cartridges dramatically increases the cost per test relative to that of high-throughput analyzers, squeezing profit margins and increasing the cost of healthcare.
The aforementioned limitations of diagnostic devices have forced many small clinics and laboratories to abandon on-site testing in favour of testing in a centralized laboratory. A centralized laboratory typically uses HTS analyzers to perform tests on samples culled from a number of smaller clinics. This process is costly and time consuming, as it necessitates the shipping of samples from the clinic to the centralized laboratory. Although an individual test may only take minutes to complete by the analyzer in the laboratory, the time interval between shipping the sample and receiving the report can be days. To make matters worse, the assays performed on the large analyzers are usually only semi-quantitative tests that are susceptible to problems associated with matrix effects, sample adulteration and poor specificity. These problems commonly lead to the reporting of false positive results, in which case it is often necessary to perform further quantitative confirmatory testing, leading to further costs and delays.
There is therefore a need for a diagnostic analyzer that bridges the existing gap between HTS and point-of-care analyzers, providing an analyzer that offers moderate throughput, ease of use by unskilled workers, minimal sample handling, low consumable cost and assay versatility in a compact and inexpensive instrument.